The present invention relates to trailer safety and in particular, to the safety of trailers towed behind road vehicles.
In this document, the term xe2x80x9ctrailerxe2x80x9d will be used to encompass caravans, trailers and other like arrangements. When towing a trailer on the road, particularly behind a private vehicle, it is common to use a single point towing hitch, commonly known as a tow ball. This arrangement provides safe control over the trailer when the towing vehicle is accelerating, so that positive forces are being applied to the trailer through the hitch. However, when the towing vehicle stops accelerating, the trailer is no longer stabilised in this manner and can begin to sway dangerously, particularly when the towing vehicle decelerates.
Systems are known which determine lateral sway or acceleration of a vehicle during cornering and then selectively apply braking to control that sway. An example of such a system is given in U.S. Pat. No. 4,023,864 (Lang et al). Unfortunately, lateral sway is only one form of vehicle instability and may not be a significant factor with vehicle stability when travelling in a straight line. Furthermore, it would be desirable to detect and prevent vehicle instability before there is lateral sway.
The present invention provides a trailer control system comprising sensor means operable to measure forces between the towing vehicle and the trailer, control means operable while the vehicle is in operation and in response to the measurements to assess the behaviour of the trailer relative to the towing vehicle, the control means being further operable to apply braking to the trailer to modify the trailer behaviour independently of operation of the vehicle brakes by the operator whereby at least load axially applied to the vehicle by the trailer is continuously assessed, and the control means thereby applies braking to substantially ensure that the load remains positive.
Preferably the system calculates whether or not towing forces are being applied to the trailer. The trailer may be operable to apply braking if towing forces are not being applied. Braking may be applied until towing forces are restored. Braking is preferably enabled and disabled in pulsed manner until towing forces are restored.
The sensor means may provide information enabling the system to detect the alignment of the trailer behind the towing vehicle. The system may be operable to apply braking selectively to one side of the trailer or the other to correct misalignment. The sensor means may provide information enabling the system to sense the vehicle turning. Preferably the system refrains from applying braking to the trailer while the vehicle is turning.
The sensor means are preferably arranged to sense forces in the mounting arrangement by which the trailer hitch point is mounted on the towing vehicle. The sensor means may comprise a spacer member which, in use, is entrapped between the towing vehicle and the trailer hitch point, and transducer means operable to detect forces within the spacer member. The transducer means may comprise strain gauges, which are preferably under compression when the system is at rest. The transducer means may comprise a plurality of transducers distributed around the spacer member. The system may further comprise accelerometer means operable to measure acceleration of the towing vehicle and/or trailer. Preferably the accelerometer means measure acceleration of the towing vehicle, and derive the acceleration of the trailer from the measured acceleration and from the force measurements of the sensor means.
The system may further comprise actuator means operable to apply control forces to a brake cable of the trailer. The actuator means may comprise at least one stepper motor. The actuator means may be operable to apply control forces independently to individual brake cables.